Polylactic acid composite film and its preparation method and application

Abstract

The present invention provides a polylactic acid composite film, a preparation method and application thereof, wherein the polylactic acid composite film comprises a polylactic acid fiber film, the surface of the polylactic acid fiber film is coated with a polydopamine coating, and the surface of the polydopamine coating is distributed with hydroxyapatite nanowires. In the present invention, the surface of the polylactic acid fiber film is first coated with a polydopamine coating, and then the hydroxyapatite nanowires are distributed on the surface of the polydopamine coating by means of intermolecular forces. In this way, the polydopamine coating can, on the one hand, improve the hydrophobic properties of the polylactic acid fiber film, thereby increasing the interfacial bonding force between the hydroxyapatite nanowires and the polylactic acid fiber film; on the other hand, there is a van der Waals hydrogen bonding effect between the polydopamine coating and the electret of the hydroxyapatite nanowires, so that the polydopamine coating can maintain a close connection with the hydroxyapatite nanowires, thereby enabling the hydroxyapatite nanowires to be stably and evenly dispersed on the polylactic acid fiber film.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane materials, and in particular to a polylactic acid composite membrane and a preparation method and application thereof. Background Art

[0002] With the development of the times, air pollution caused by automobile exhaust, industrial waste gas emissions, etc. has become a problem that cannot be ignored. Among them, the diameter of particles floating in the air is less than 2.5 microns (PM 2.5 ) and less than 10 microns (PM 10 ) particles can easily invade the human respiratory system. Long-term exposure to such an environment will cause health problems, and air filtration is a key link and effective method to improve air quality.

[0003] At present, the portable air filter materials on the market mainly include ordinary gauze, filter cotton and non-woven fabrics. Ordinary gauze, non-woven fabrics and other air filter materials are more commonly used. Their fiber diameter is relatively coarse and the pores between the fiber structures are too large. They mainly rely on mechanical interception such as Brownian diffusion, interception, inertial collision, gravity sedimentation to filter particles in the air. They have good filtering effect on particles larger than 10 microns, but have poor filtering effect on fine particles PM. 2.5 The filtration efficiency is low. And since most filter materials (such as traditional petroleum-based materials) are still non-degradable materials, they will inevitably cause environmental problems. At the same time, due to the substantial increase in the use of medical surgical masks in recent years, the production of biodegradable air filter materials has become a new trend, such as polylactic acid membrane materials. Usually when using polylactic acid membrane materials, in order to improve the filtration performance of the membrane material, some electret materials are usually added to it for compounding, because the electret material can effectively intercept tiny particles through the electrostatic effect.

[0004] As a natural bioelectret material, hydroxyapatite has excellent biocompatibility and can maintain a polarized or charged state for a long time, which makes it possible to prepare long-lasting filter materials. However, hydroxyapatite exhibits irregular morphology under different conditions, such as granular, needle-shaped or flake-shaped, and is not suitable for the preparation of filter materials with high flexibility requirements. Moreover, the traditional method of synthesizing hydroxyapatite takes a long time. Generally, the method of synthesizing hydroxyapatite nanowires mainly adopts solvothermal method or hydrothermal method. For example, patent number ZL201310687363.2 discloses that the solvothermal method often requires a solvothermal reaction at 100-220°C for 24 hours, which makes it difficult to achieve efficient synthesis.

[0005] Hydroxyapatite nanowires, due to their nanoscale and high ion activity, can be used to prepare highly flexible filter materials (such as polymer-based membranes, ceramic-based membranes, and carbon-based membranes), which can achieve high surface potential and excellent filtering effects of the filter materials. However, hydroxyapatite nanowires are small in size and high in surface energy, and are easily agglomerated in the filter material, resulting in poor dispersibility, which makes it difficult to effectively improve the filtering performance of the filter material. In the prior art, ultrasonic dispersion is usually directly used to disperse hydroxyapatite nanowires, but the dispersion effect is still poor. Due to their small size and high surface energy, hydroxyapatite nanowires are easily agglomerated after centrifugation. Even after ultrasonic treatment, it is still difficult to achieve the effect of long-term stable dispersion of the nanowires in the aqueous solution, which in turn makes it difficult to effectively improve the filtering performance of the filter material.

[0006] Therefore, it is necessary to provide a polylactic acid composite membrane and a preparation method thereof to solve the problem in the prior art that the bioelectret is poorly dispersed and easily agglomerated in the filter material, resulting in poor filtration improvement of the product. Summary of the Invention

[0007] The main purpose of the present invention is to provide a polylactic acid composite membrane and its preparation method and application, so as to solve the problem in the prior art that the bioelectret is poorly dispersed and easily agglomerated in the filter material, resulting in poor product filtration improvement effect.

[0008] To achieve the above object, according to one aspect of the present invention, a polylactic acid composite film is provided, comprising a polylactic acid fiber film, the surface of the polylactic acid fiber film is coated with a polydopamine coating, and hydroxyapatite nanowires are distributed on the surface of the polydopamine coating.

[0009] Furthermore, the weight content of hydroxyapatite nanowires in the polylactic acid composite film is 0.05 to 40 wt%, more preferably 0.5 to 20 wt%.

[0010] Furthermore, the weight content of the polydopamine coating in the polylactic acid composite film is 0.01 to 10 wt%, and more preferably 0.1 to 5 wt%.

[0011] Furthermore, the thickness of the polylactic acid fiber membrane is 40 to 800 μm, and the fiber diameter of the polylactic acid fiber membrane is 5 to 60 μm.

[0012] Furthermore, the thickness of the polydopamine coating is 40 to 300 nm.

[0013] Furthermore, the diameter of the hydroxyapatite nanowires is 1 to 200 nm.

[0014] Furthermore, the aspect ratio of the hydroxyapatite nanowires is 5 to 200:1, and more preferably 80 to 150:1.

[0015] To achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing a polylactic acid composite film is provided, comprising: providing a polylactic acid fiber film; coating the surface of the polylactic acid fiber film with a polydopamine coating; and distributing hydroxyapatite nanowires on the surface of the polydopamine coating to obtain a polylactic acid composite film.

[0016] Furthermore, the preparation method of the polylactic acid composite membrane includes: placing the polylactic acid fiber membrane in a buffer solution containing dopamine and / or dopamine derivatives for immersion, so that the dopamine and / or dopamine derivatives are polymerized to form polydopamine, and the polydopamine is coated on the surface of the polylactic acid fiber membrane, and after drying, a polylactic acid fiber membrane with a surface coated with a polydopamine coating is obtained.

[0017] Furthermore, the immersion treatment time is 4 to 36 hours, and the treatment temperature is 25 to 60°C.

[0018] Furthermore, the amount of the buffer solution used is 100 to 3000 mL per cubic meter of the polylactic acid fiber membrane; more preferably 1000 to 2500 mL.

[0019] Furthermore, the mass concentration of dopamine and / or dopamine derivatives in the buffer solution is 0.5 to 100 mg / mL; more preferably 0.5 to 30 mg / mL.

[0020] Furthermore, the solvent in the buffer solution is tris(hydroxymethyl)aminomethane buffer; more preferably, the pH of the tris(hydroxymethyl)aminomethane buffer is 8-10.

[0021] Furthermore, the dopamine derivative is selected from one or more of dopamine hydrochloride, levodopa, N-methyldopamine, 3-methacryloyldopamine or catechol.

[0022] Furthermore, the dispersion containing hydroxyapatite nanowires is distributed on the surface of the polydopamine coating by one or more methods including atomization, vacuum filtration, immersion or electrophoretic deposition.

[0023] Furthermore, the dispersion containing hydroxyapatite nanowires is obtained by the following preparation method: dispersing hydroxyapatite nanowires in a dispersant and performing shear grinding to obtain the dispersion containing hydroxyapatite nanowires.

[0024] Furthermore, the dispersant is selected from one or more of ethanol, water, polyvinyl pyrrolidone, dodecyltrimethylammonium bromide, sodium lauryl sulfate or sodium dodecylbenzenesulfonate.

[0025] Furthermore, the linear speed of the shear grinding is 15 to 40 m / s; and the time of the shear grinding is 10 to 120 min.

[0026] Furthermore, the solid content of the dispersion containing hydroxyapatite nanowires is 1 to 15 wt %.

[0027] Furthermore, the shear grinding is performed in a high-speed shear grinding device, and the energy consumption per unit mass of the high-speed shear grinding device is 0.5 to 10 kWh / kg.

[0028] Furthermore, hydroxyapatite nanowires are prepared by the following method: fatty acids, alcohol solvents, alkaline solutions, water-soluble calcium salt solutions, and water-soluble phosphate solutions are mixed and placed in a microwave reactor for biomimetic mineralization reaction to obtain hydroxyapatite nanowires.

[0029] Furthermore, the fatty acid and alcohol solvent are first mixed, and then an alkaline solution and a water-soluble calcium salt solution are added under stirring conditions to react to generate a fatty acid calcium precursor; the fatty acid calcium precursor and the water-soluble phosphate solution are then mixed and placed in a microwave reactor, and a biomimetic mineralization reaction is carried out under stirring conditions to obtain hydroxyapatite nanowires.

[0030] Furthermore, the fatty acid is selected from one or more of stearic acid, lauric acid, oleic acid, linoleic acid or linolenic acid.

[0031] Furthermore, the alcohol solvent is selected from one or more of ethanol, methanol, propanol, isopropanol or butanol.

[0032] Furthermore, the alkaline solution is selected from a sodium hydroxide aqueous solution, and the molar concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 0.01 to 10 mol / L.

[0033] Furthermore, the water-soluble calcium salt solution is selected from one or more of a calcium chloride aqueous solution, a calcium nitrate aqueous solution, a calcium acetate aqueous solution or a calcium hypochlorite aqueous solution.

[0034] Furthermore, the water-soluble phosphate solution is selected from one or more of an aqueous solution of ammonium dihydrogen phosphate, an aqueous solution of ammonium hydrogen phosphate, an aqueous solution of sodium dihydrogen phosphate, an aqueous solution of sodium dihydrogen phosphate, an aqueous solution of dipotassium hydrogen phosphate or an aqueous solution of potassium dihydrogen phosphate.

[0035] Furthermore, the molar concentration of calcium ions in the water-soluble calcium salt solution is 0.01 to 2 mol / L.

[0036] Furthermore, the molar ratio of calcium ions in the water-soluble phosphate solution to phosphate ions in the water-soluble phosphate solution is 1 to 2:1.

[0037] Furthermore, the reaction temperature of the biomimetic mineralization reaction is 100-250° C., and the reaction time is 1-60 min.

[0038] According to another aspect of the present invention, there is provided an application of a polylactic acid composite membrane in an air filter material.

[0039] Applying the technical solution of the present invention, the present invention proposes adding hydroxyapatite nanowires to a polylactic acid fiber membrane to enhance the filtration performance of the fiber membrane material. Specifically, to enhance the bonding strength between the hydroxyapatite nanowires and the polylactic acid fiber membrane and the uniform dispersion of the hydroxyapatite nanowires, the present invention first coats the surface of the polylactic acid fiber membrane with a polydopamine coating, and then distributes the hydroxyapatite nanowires on the surface of the polydopamine coating through intermolecular forces. This polydopamine coating improves the hydrophobicity of the polylactic acid fiber membrane, thereby increasing the interfacial bonding strength between the hydroxyapatite nanowires and the polylactic acid fiber membrane. Furthermore, van der Waals hydrogen bonding occurs between the polydopamine coating and the hydroxyapatite nanowire electrets, maintaining a tight connection between the polydopamine coating and the hydroxyapatite nanowires, thereby ensuring a stable and uniform dispersion of the hydroxyapatite nanowires on the polylactic acid fiber membrane. By coating the polylactic acid fiber membrane with a polydopamine coating, the agglomeration of hydroxyapatite nanowires is effectively avoided, the interfacial compatibility with the polylactic acid fiber membrane is improved, stress dispersion is promoted, and the mechanical properties of the product are improved; at the same time, the uniformly dispersed hydroxyapatite nanowires can give full play to their performance, prolong the time for the polylactic acid fiber membrane to store charge, generate a stable electrostatic field on the surface of the polylactic acid fiber membrane, and manifest as a material with a high surface potential, enhance the electrostatic adsorption of submicron particles, so that the product can maintain excellent long-term filtration and filtration efficiency. Moreover, the polylactic acid fiber membrane, polydopamine coating and hydroxyapatite nanowires also have excellent biocompatibility and biodegradability, and the polylactic acid composite membrane obtained by the composite also has excellent biocompatibility and biodegradability. At the same time, the hydroxyapatite nanowires in the polylactic acid composite membrane can maintain a polarized or charged state for a long time, prolonging the fiber. This allows the polylactic acid composite membrane to obtain a higher surface potential, thereby enabling electrostatic adsorption of submicron particles. In summary, the polylactic acid composite membrane of the present invention has excellent surface potential, mechanical properties, filtration efficiency and long-term filtration performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0041] Figure 1 A schematic diagram showing a process for preparing a polylactic acid composite film in one embodiment of the present invention is shown;

[0042] Figure 2 A scanning electron microscope image (magnification of 40K) of hydroxyapatite nanowires synthesized in Example 3 of the present invention is shown;

[0043] Figure 3A scanning electron microscope image (magnification of 40K) of hydroxyapatite nanowires in a dispersion containing hydroxyapatite nanowires prepared in Example 3 of the present invention is shown. DETAILED DESCRIPTION

[0044] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0045] As described in the background section of this application, prior art techniques have limited effectiveness in improving product filtration due to poor dispersion and aggregation of bioelectrets in filter materials. To address this issue, this application provides a polylactic acid composite membrane comprising a polylactic acid fiber membrane having a polydopamine coating disposed on its outer surface, and hydroxyapatite nanowires distributed on the surface of the polydopamine coating.

[0046] To improve the filtration performance of fiber membrane materials, prior art typically adds electret materials (such as hydroxyapatite nanowires) during the electrospinning process to impart a higher surface potential to the fiber membrane filter material, thereby enhancing filtration performance and efficiency. However, the applicant has discovered that these electret materials (such as hydroxyapatite nanowires) tend to aggregate within the fiber membrane filter material, resulting in poor filtration performance improvements.

[0047] Based on this, the present invention proposes to add hydroxyapatite nanowires to the polylactic acid fiber membrane to improve the filtration performance of the fiber membrane material. In particular, when adding hydroxyapatite nanowires, in order to improve the bonding strength between the hydroxyapatite nanowires and the polylactic acid fiber membrane and the uniform dispersion of the hydroxyapatite nanowires, the present invention first coats the surface of the polylactic acid fiber membrane with a polydopamine coating, and then distributes the hydroxyapatite nanowires on the surface of the polydopamine coating through intermolecular forces. In this way, the polydopamine coating can improve the hydrophobic properties of the polylactic acid fiber membrane, thereby increasing the interfacial bonding strength between the hydroxyapatite nanowires and the polylactic acid fiber membrane; on the other hand, there is a van der Waals hydrogen bonding between the polydopamine coating and the hydroxyapatite nanowire electret, which enables the polydopamine coating to maintain a close connection with the hydroxyapatite nanowires, thereby promoting the hydroxyapatite nanowires to be stably and evenly dispersed on the polylactic acid fiber membrane. By coating the polylactic acid fiber membrane with a polydopamine coating, the agglomeration of hydroxyapatite nanowires is effectively avoided, the interfacial compatibility with the polylactic acid fiber membrane is improved, stress dispersion is promoted, and the mechanical properties of the product are improved; at the same time, the evenly dispersed hydroxyapatite nanowires can give full play to their properties, prolong the time for the polylactic acid fiber membrane to store charge, generate a stable electrostatic field on the surface of the polylactic acid fiber membrane, and manifest as a material with a higher surface potential, thereby enhancing the electrostatic adsorption of submicron particles, so that the product can maintain better long-term filtration and filtration efficiency.

[0048] Moreover, the polylactic acid fiber membrane, polydopamine coating, and hydroxyapatite nanowires also have excellent biocompatibility and biodegradability, and the resulting polylactic acid composite membrane also has excellent biocompatibility and biodegradability. At the same time, the hydroxyapatite nanowires in the polylactic acid composite membrane can maintain a polarized or charged state for a long time, extending the fiber life. This allows the polylactic acid composite membrane to obtain a higher surface potential, thereby enabling electrostatic adsorption of submicron particles.

[0049] The polylactic acid composite membrane of the invention has excellent surface potential, mechanical properties, filtration efficiency and long-term filtration performance.

[0050] To further improve the filtration performance of the polylactic acid composite membrane, the weight of the hydroxyapatite nanowires in the polylactic acid composite membrane is preferably 0.05 to 40 wt%, for example, 0.05 wt%, 0.5 wt%, 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%. More preferably, the weight is 0.5 to 20 wt%. If the weight of the hydroxyapatite nanowires is too high, agglomeration of the hydroxyapatite nanowires may occur, resulting in a decrease in the filtration performance of the polylactic acid composite membrane. If the weight of the hydroxyapatite nanowires is too low, the polylactic acid composite membrane cannot achieve a high surface potential, and its adsorption capacity for submicron particles is reduced.

[0051] In a preferred embodiment, the weight of the polydopamine coating in the polylactic acid composite membrane is 0.01 to 10 wt%, for example, 0.01 wt%, 0.1 wt%, 1 wt%, 2 wt%, 5 wt%, 6 wt%, 8 wt%, or 10 wt%. By limiting the weight of the polydopamine coating to the above range, the present invention can further enhance the connection between the polydopamine coating and the hydroxyapatite nanowires, allowing the hydroxyapatite nanowires to be more evenly and stably dispersed on the polylactic acid fiber membrane, thereby enabling the polylactic acid composite membrane to have better long-term filtration, mechanical properties, and filtration performance. More preferably, the weight is 0.1 to 5 wt%.

[0052] In a preferred embodiment, the thickness of the polylactic acid fiber membrane is 40 to 800 μm, for example, 40 μm, 80 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, and 800 μm. The fiber diameter of the polylactic acid fiber membrane is 5 to 60 μm, for example, 5 μm, 10 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, and 60 μm. The present invention controls the thickness and fiber diameter of the polylactic acid fiber membrane within the above ranges to improve the filtration performance of the polylactic acid composite membrane, control the operating cost of the filtration process, and facilitate subsequent practical production applications. If the thickness of the polylactic acid fiber membrane is too high, the pressure drop during the filtration process will be too high, the operating cost will be too high, and it will be unfavorable for subsequent practical applications; if the thickness of the polylactic acid fiber membrane is too low, the mechanical properties of the membrane will be reduced, thereby shortening the service life of the membrane. If the fiber diameter of the polylactic acid fiber membrane is too high, it will affect the uniformity inside the fiber membrane and reduce the porosity of the fiber membrane, resulting in excessive pressure drop during the filtration process, which is not conducive to subsequent practical applications; if the diameter of the polylactic acid fiber membrane is too low, the porosity of the fiber membrane will be too high, reducing the physical interception efficiency.

[0053] In order to further improve the filtration performance of the polylactic acid composite membrane, preferably the thickness of the polylactic acid fiber membrane is 100 to 800 μm, and the fiber diameter of the polylactic acid fiber membrane is 5 to 20 μm.

[0054] In a preferred embodiment, the thickness of the polydopamine coating is 40 to 300 nm, for example, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 150 nm, 200 nm, 250 nm, or 300 nm. When the thickness of the polydopamine coating is too high, it will affect the uniformity of the coating and reduce the uniformity of the dispersion of the hydroxyapatite nanowires; when the thickness is too low, it will be difficult to effectively fix the hydroxyapatite nanowires. The present invention controls the thickness of the polydopamine coating to 40 to 300 nm, which allows the hydroxyapatite nanowires to be more firmly and evenly dispersed on the surface of the polydopamine coating, further improving the long-term filtration, mechanical properties, and filtration performance of the polylactic acid composite membrane.

[0055] In a preferred embodiment, the diameter of the hydroxyapatite nanowires is 1 to 200 nm. By limiting the diameter of the hydroxyapatite nanowires to the above range, the present invention enables the hydroxyapatite nanowires to be more evenly and stably dispersed on the polylactic acid fiber membrane. More preferably, the diameter is 80 to 200 nm.

[0056] In order to further improve the dispersibility of the hydroxyapatite nanowires, the aspect ratio of the hydroxyapatite nanowires is preferably 5 to 200:1, more preferably 80 to 200:1.

[0057] Another aspect of the present invention provides a method for preparing a polylactic acid composite film, such as Figure 1 As shown, the preparation method includes: providing a polylactic acid fiber membrane; coating the surface of the polylactic acid fiber membrane with a polydopamine coating; distributing hydroxyapatite nanowires on the surface of the polydopamine coating to obtain a polylactic acid composite membrane.

[0058] Based on the above reasons, the polylactic acid fiber membrane prepared by the present invention has excellent long-term filtration, mechanical properties, and filtration performance.

[0059] In a preferred embodiment, specifically, a polylactic acid fiber membrane is immersed in a buffer solution containing dopamine monomer and / or dopamine derivative monomer, so that the dopamine monomer and / or dopamine derivative monomer undergoes polymerization to form polydopamine, and the polydopamine is coated on the surface of the polylactic acid fiber membrane. After drying, a polylactic acid fiber membrane with a polydopamine coating on the surface is obtained. The present invention can use the above method to obtain a polylactic acid fiber membrane with a polydopamine coating on the surface, or other conventional methods in the art, such as blade coating, can also be used.

[0060] In order to further obtain a more suitable thickness and more uniform polydopamine coating, the immersion treatment time is preferably 4 to 36 hours and the treatment temperature is 25 to 60° C. Preferably, the amount of the buffer solution used is 100 to 1000 mL per cubic meter of the polylactic acid fiber membrane.

[0061] In a preferred embodiment, the mass concentration of dopamine and / or dopamine derivatives in the buffer solution is 0.5 to 100 mg / mL. The deposition rate of polydopamine increases with increasing concentration of the precursor dopamine / dopamine derivative. When the concentration is too high, the deposition rate of polydopamine does not change significantly. Therefore, controlling the mass concentration of dopamine and / or dopamine derivatives in the buffer solution to 0.5 to 100 mg / mL achieves a relatively suitable polydopamine deposition rate and is most economical.

[0062] In order to further obtain a polyamine coating with better performance, the solvent in the buffer solution is tris(hydroxymethyl)aminomethane buffer; more preferably, the pH of the tris(hydroxymethyl)aminomethane buffer is 8-10.

[0063] In order to further obtain a polypolyamine coating with better performance, the dopamine derivative in the buffer solution is selected from one or more of dopamine hydrochloride (such as CAS number: 62-31-7), levodopa (such as CAS number: 59-92-7), N-methyldopamine (such as CAS number: 62-32-8), 3-methacryloyldopamine (such as CAS number: 471915-89-6), hydroquinone (such as CAS number: 123-31-9) or catechol (such as CAS number: 120-80-9).

[0064] In a preferred embodiment, a dispersion containing hydroxyapatite nanowires is distributed on the surface of the polydopamine coating by one or more of atomization, vacuum filtration, immersion, or electrophoretic deposition. The present invention utilizes the above-described methods to distribute the dispersion containing hydroxyapatite nanowires on the surface of the polydopamine coating, thereby promoting uniform distribution of the hydroxyapatite nanowires on the surface of the polydopamine coating and effectively utilizing the high surface potential and high ionic activity of the hydroxyapatite nanowires.

[0065] Preferably, the dispersion containing hydroxyapatite nanowires is prepared by the following preparation method: dispersing hydroxyapatite nanowires in water and subjecting them to shear grinding to obtain a dispersion containing hydroxyapatite nanowires. This method can promote surface activation of the hydroxyapatite nanowires and enhance the uniform dispersion of the hydroxyapatite nanowires in the dispersion, thereby uniformly distributing the hydroxyapatite nanowires on the polydopamine coating and stably attaching the hydroxyapatite nanowires to the polylactic acid composite membrane, thereby improving the filtration performance of the polylactic acid composite membrane.

[0066] In order to further improve the surface activation of hydroxyapatite nanowires and the dispersibility of hydroxyapatite nanowires in the dispersion, the shear grinding linear speed is preferably 15 to 40 m / s; the shear grinding time is 10 to 120 min; and the solid content of the dispersion containing hydroxyapatite nanowires is preferably 1 to 15 wt%.

[0067] To further improve shear grinding efficiency, shear grinding is performed in a high-speed shear grinding device with a unit mass energy consumption of 0.5 to 10 kWh / kg. Specifically, the high-speed shear grinding device is one or more of a shear emulsifier, an inline shear dispersing emulsifier, a vacuum homogenizer, a pin sand mill, or a turbine sand mill.

[0068] In order to further improve the structural regularity and uniformity of hydroxyapatite nanowires, promote their more uniform dispersion on the surface of the polylactic acid composite film, and better exert the efficacy of the bioelectret, the hydroxyapatite nanowires of the present invention are prepared by the following method: fatty acids, alcohol solvents, alkaline solutions, water-soluble calcium salt solutions, and water-soluble phosphate solutions are mixed and placed in a microwave reactor for biomimetic mineralization reaction to obtain hydroxyapatite nanowires.

[0069] Preferably, a fatty acid and an alcohol solvent are first mixed, and then an alkaline solution and a water-soluble calcium salt solution are added under stirring to react and generate a fatty acid calcium precursor; the fatty acid calcium precursor and a water-soluble phosphate aqueous solution are then mixed and placed in a microwave reactor, and a biomimetic mineralization reaction is carried out under stirring to obtain hydroxyapatite nanowires. The above method for synthesizing hydroxyapatite nanowires has the advantages of high yield and short synthesis time, and the synthesized hydroxyapatite nanowires have a more regular and uniform morphology.

[0070] In a preferred embodiment, the fatty acid is selected from one or more of stearic acid, lauric acid, oleic acid, linoleic acid, or linolenic acid. The use of these fatty acids in the present invention can more effectively regulate the synthesis rate of hydroxyapatite nanowires and control the crystal morphology of the hydroxyapatite nanowires, further improving the crystallinity of the hydroxyapatite nanowires and promoting their dispersion.

[0071] In order to further improve the synthesis efficiency of hydroxyapatite nanowires, the alcohol solvent is selected from one or more of ethanol, methanol, propanol, isopropanol and butanol; preferably, the water-soluble calcium salt solution is selected from one or more of calcium chloride aqueous solution, calcium nitrate aqueous solution, calcium acetate aqueous solution or calcium hypochlorite aqueous solution; preferably, the water-soluble phosphate solution is selected from one or more of ammonium dihydrogen phosphate aqueous solution, ammonium hydrogen phosphate aqueous solution, sodium dihydrogen phosphate aqueous solution, sodium dihydrogen phosphate aqueous solution, dipotassium hydrogen phosphate aqueous solution or potassium dihydrogen phosphate aqueous solution.

[0072] In a preferred embodiment, the alkaline solution is selected from an aqueous sodium hydroxide solution, and the molar concentration of sodium hydroxide in the aqueous sodium hydroxide solution is 0.01 to 10 mol / L. The use of an aqueous sodium hydroxide solution in the present invention can adjust the pH value of the reaction system to promote the synthesis of hydroxyapatite nanowires. Simultaneously, limiting the molar concentration can effectively adjust the concentrations of calcium and phosphorus ions in the hydroxyapatite nanowire reaction system, resulting in a more uniform morphology and improved crystallinity. Further preferably, the molar concentration of sodium hydroxide in the aqueous sodium hydroxide solution is 0.01 to 4 mol / L.

[0073] In some preferred embodiments, the molar concentration of calcium ions in the water-soluble calcium salt solution is preferably 0.01 to 2 mol / L; the molar ratio of calcium ions in the water-soluble phosphate solution to phosphate ions in the water-soluble phosphate solution is preferably 1 to 2:1; the reaction temperature of the biomimetic mineralization reaction is preferably 100 to 250°C, and the reaction time is 1 to 60 minutes. The present invention employs the above-mentioned conditions and parameters to obtain hydroxyapatite nanowires with more regular and uniform morphology. Compared with traditional solvothermal or hydrothermal methods, the synthesis of hydroxyapatite nanowires using microwave-assisted biomimetic mineralization reaction has a shorter synthesis time and a higher product yield.

[0074] The present invention also provides an application of the polylactic acid composite membrane in air filter materials.

[0075] Based on the above reasons, the polylactic acid composite membrane of the present invention is particularly suitable for air filter materials, which has a high surface potential and is effective for fine particulate matter PM. 2.5 The polylactic acid composite membrane has high filtration efficiency, high mechanical strength and can filter for a long time. It is also biodegradable and has broad market application prospects.

[0076] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0077] Example 1

[0078] Preparation of hydroxyapatite nanowires: Calcium chloride (0.51 g) and sodium hydroxide (1 g) were added to 20 mL of deionized water to prepare a calcium chloride aqueous solution (the molar concentration of calcium ions was 0.23 mol / L) and a sodium hydroxide aqueous solution (the molar concentration of sodium hydroxide was 1.25 mol / L), respectively; the calcium chloride aqueous solution and the sodium hydroxide aqueous solution were added dropwise to a mixed solution of 12 g of anhydrous ethanol and 12 g of oleic acid at room temperature while stirring; then 10 mL of sodium dihydrogen phosphate aqueous solution (the molar concentration of phosphate ions was 0.23 mol / L) was added dropwise to the above solution, mixed evenly, and then placed in a microwave reactor, and a biomimetic mineralization reaction occurred under stirring conditions at a temperature of 180° C. and a reaction time of 30 minutes. After the reaction, the reaction precipitate was washed and dried to obtain hydroxyapatite nanowires;

[0079] Preparation of a dispersion containing hydroxyapatite nanowires: Dispersing the hydroxyapatite nanowires in water and subjecting them to shear grinding using a turbine sand mill (energy consumption per unit mass: 1 kWh / kg, temperature: 25° C.), wherein the shear grinding speed is 20 m / s, and the shear grinding time is 30 minutes to obtain a dispersion containing hydroxyapatite nanowires (solids content: 2 wt%).

[0080] Preparation of a polylactic acid fiber membrane coated with a polydopamine coating: 0.2 g of dopamine hydrochloride (CAS No. 62-31-7) was weighed and dissolved in a tris (hydroxymethylaminomethane) buffer solution (pH 8.5, tris (hydroxymethylaminomethane) mass concentration of 2 mg / mL) to obtain a buffer solution containing a dopamine derivative, wherein the mass concentration of dopamine hydrochloride was 2 mg / mL;

[0081] A polylactic acid fiber membrane (fiber diameter of 5 μm, thickness of 0.8 mm) was immersed in the above-mentioned buffer solution containing the dopamine derivative. The immersion treatment time was 4 hours, the treatment temperature was 25° C., and the amount of the buffer solution containing the dopamine derivative was 300 mL per cubic meter of the polylactic acid fiber membrane. After the immersion, excess buffer and impurities were removed, and after drying, a polylactic acid fiber membrane with a surface coated with polydopamine was obtained.

[0082] Preparation of polylactic acid composite membrane: the dispersion containing hydroxyapatite nanowires prepared above is distributed on the surface of the polydopamine coating by vacuum filtration, and then dried to obtain the polylactic acid composite membrane.

[0083] The polylactic acid composite film prepared by the above preparation method comprises: the weight of hydroxyapatite nanowires in the polylactic acid composite film is 0.5wt%, the weight of the polydopamine coating in the polylactic acid composite film is 0.1wt%, the thickness of the polydopamine coating is 0.1μm; the diameter of the hydroxyapatite nanowires is 50nm; and the aspect ratio of the hydroxyapatite nanowires is 200:1.

[0084] Example 2

[0085] Preparation of hydroxyapatite nanowires: Calcium nitrate (1.47 g) and sodium hydroxide (1 g) were added to 20 mL of deionized water to prepare a calcium nitrate aqueous solution (the molar concentration of calcium ions was 0.46 mol / L) and a sodium hydroxide aqueous solution (the molar concentration of sodium hydroxide was 1.25 mol / L); the calcium chloride aqueous solution and the sodium hydroxide aqueous solution were added dropwise to a mixed solution of 12 g of anhydrous ethanol and 12 g of oleic acid at room temperature while stirring; then 10 mL of sodium dihydrogen phosphate aqueous solution (the molar concentration of phosphate ions was 0.23 mol / L) was added dropwise to the above solution, mixed evenly, and then placed in a microwave reactor for a biomimetic mineralization reaction under stirring at 100° C. for 30 minutes. After the reaction, the reaction precipitate was washed and dried to obtain hydroxyapatite nanowires;

[0086] Preparing a dispersion containing hydroxyapatite nanowires: dispersing the hydroxyapatite nanowires in water and subjecting them to shear grinding using a shear emulsifier homogenizer (energy consumption per unit mass: 5 kWh / kg, temperature: 25° C.), wherein the shear grinding speed is 30 m / s and the shear grinding time is 30 minutes; thereby obtaining a dispersion containing hydroxyapatite nanowires (solids content: 8 wt%);

[0087] Preparation of a polylactic acid fiber membrane coated with a polydopamine coating: 0.2 g of levodopa (CAS number: 59-92-7) was weighed and dissolved in a tris buffer solution (pH 8.5, mass concentration of tris 2 mg / mL) to obtain a buffer solution containing a dopamine derivative, wherein the mass concentration of levodopa was 2 mg / mL;

[0088] A polylactic acid fiber membrane (fiber diameter of 15 μm, thickness of 0.3 mm) was immersed in the above-mentioned buffer solution containing the dopamine derivative. The immersion treatment time was 12 h, the treatment temperature was 25° C., and the amount of the buffer solution containing the dopamine derivative was 1500 mL per cubic meter of the polylactic acid fiber membrane. After the immersion, excess buffer and impurities were removed, and after drying, a polylactic acid fiber membrane with a surface coated with polydopamine was obtained.

[0089] Preparation of polylactic acid composite membrane: the dispersion containing hydroxyapatite nanowires prepared above is distributed on the surface of the polydopamine coating by vacuum filtration, and then dried to obtain the polylactic acid composite membrane.

[0090] The polylactic acid composite film prepared by the above preparation method comprises: the weight of hydroxyapatite nanowires in the polylactic acid composite film is 10wt%, the weight of the polydopamine coating in the polylactic acid composite film is 8wt%, the thickness of the polydopamine coating is 0.25μm; the diameter of the hydroxyapatite nanowires is 50nm; and the aspect ratio of the hydroxyapatite nanowires is 150:1.

[0091] Example 3

[0092] Preparation of hydroxyapatite nanowires: Calcium acetate (1.10 g) and sodium hydroxide (1 g) were added to 20 mL of deionized water to prepare a calcium nitrate aqueous solution (the molar concentration of calcium ions was 0.35 mol / L) and a sodium hydroxide aqueous solution (the molar concentration of sodium hydroxide was 1.25 mol / L); the calcium nitrate aqueous solution and the sodium hydroxide aqueous solution were added dropwise to a mixed solution of 12 g of methanol and 12 g of oleic acid at room temperature while stirring; then 10 mL of sodium dihydrogen phosphate aqueous solution (the molar concentration of phosphate ions was 0.23 mol / L) was added dropwise to the above solution, mixed well, and placed in a microwave reactor for a biomimetic mineralization reaction under stirring at a temperature of 150° C. for 15 minutes. After the reaction, the precipitate was washed and dried to obtain hydroxyapatite nanowires;

[0093] Preparation of a dispersion containing hydroxyapatite nanowires: The hydroxyapatite nanowires were dispersed in water and shear-milled using a pipeline shear dispersing emulsifier (energy consumption per unit mass: 8 kWh / kg, temperature: 25°C), with a shear milling speed of 35 m / s and a shear milling time of 30 minutes; to obtain a dispersion containing hydroxyapatite nanowires (solid content: 5 wt%).

[0094] Preparation of a polylactic acid fiber membrane coated with a polydopamine coating: 0.2 g of dopamine (CAS No. 51-61-6) was weighed and dissolved in a tris buffer solution (pH 8.5, tris concentration of 1 mg / mL) to obtain a dopamine-containing buffer solution with a dopamine concentration of 1 mg / mL;

[0095] A polylactic acid fiber membrane (fiber diameter of 18 μm, thickness of 0.3 mm) was immersed in the above-mentioned dopamine-containing buffer solution for 18 h at a temperature of 25° C. The amount of dopamine-containing buffer solution used per cubic meter of polylactic acid fiber membrane was 1200 mL. After the immersion, excess buffer solution and impurities were removed, and the polylactic acid fiber membrane with a polydopamine coating was obtained after drying.

[0096] Preparation of polylactic acid composite film: The dispersion containing hydroxyapatite nanowires prepared above was distributed on the surface of the polydopamine coating by atomization (flow rate of 50 mL / min), and then dried to obtain a polylactic acid composite film.

[0097] The polylactic acid composite film prepared by the above preparation method comprises: the weight of hydroxyapatite nanowires in the polylactic acid composite film is 20wt%, the weight of the polydopamine coating in the polylactic acid composite film is 5wt%, the thickness of the polydopamine coating is 0.2μm; the diameter of the hydroxyapatite nanowires is 50nm; and the aspect ratio of the hydroxyapatite nanowires is 100:1.

[0098] Example 4

[0099] Preparation of hydroxyapatite nanowires: Calcium hypochlorite (1.15 g) and sodium hydroxide (1 g) were added to 20 mL of deionized water to prepare a calcium hypochlorite aqueous solution (the molar concentration of calcium ions was 0.40 mol / L) and a sodium hydroxide aqueous solution (the molar concentration of sodium hydroxide was 1.25 mol / L), respectively. The calcium hypochlorite aqueous solution and the sodium hydroxide aqueous solution were added dropwise to a mixed solution of 12 g of methanol and 12 g of oleic acid while stirring at room temperature. Then, 10 mL of sodium dihydrogen phosphate aqueous solution (the molar concentration of phosphate ions was 0.23 mol / L) was added dropwise to the above solution. After mixing evenly, the mixture was placed in a microwave reactor and subjected to a biomimetic mineralization reaction under stirring at 200° C. for 25 minutes. After the reaction, the precipitate was washed and dried to obtain hydroxyapatite nanowires.

[0100] Preparing a dispersion containing hydroxyapatite nanowires: Dispersing the hydroxyapatite nanowires in water and subjecting them to shear grinding using a vacuum homogenizer (energy consumption per unit mass: 8 kWh / kg, temperature: 25° C.) at a linear speed of 25 m / s for 30 minutes to obtain a dispersion containing hydroxyapatite nanowires (solids content: 15 wt%).

[0101] A polylactic acid fiber membrane coated with a polydopamine coating was prepared by weighing 0.2 g of dopamine (CAS No. 51-61-6) and levodopa (CAS No. 59-92-7), respectively, and dissolving them in a tris buffer solution (pH 8.5, tris concentration of 1 mg / mL) to obtain a buffer solution containing dopamine and dopamine derivatives, wherein the concentration of dopamine and dopamine derivatives was 1 mg / mL.

[0102] The polylactic acid fiber membrane (fiber diameter of 60 μm and thickness of 0.8 mm) was placed in the above-mentioned buffer solution containing dopamine and dopamine derivatives for immersion. The immersion treatment time was 12 h and the treatment temperature was 25°C. The amount of the buffer solution containing dopamine and dopamine derivatives was 2400 mL per cubic meter of polylactic acid fiber membrane. After the immersion, the excess buffer solution and impurities were removed, and after drying, a polylactic acid fiber membrane with a surface coated with a polydopamine coating was obtained.

[0103] Preparation of polylactic acid composite film: The dispersion containing hydroxyapatite nanowires prepared above was distributed on the surface of the polydopamine coating by immersion (immersion time was 1 h), and then dried to obtain the polylactic acid composite film.

[0104] The polylactic acid composite film prepared by the above preparation method comprises: the weight of hydroxyapatite nanowires in the polylactic acid composite film is 40wt%, the weight of the polydopamine coating in the polylactic acid composite film is 10wt%, the thickness of the polydopamine coating is 0.3μm; the diameter of the hydroxyapatite nanowires is 20nm; and the aspect ratio of the hydroxyapatite nanowires is 80:1.

[0105] Example 5

[0106] Preparation of hydroxyapatite nanowires: Calcium chloride (1.01 g) and sodium hydroxide (1 g) were added to 20 mL of deionized water to prepare a calcium chloride aqueous solution (the molar concentration of calcium ions was 0.46 mol / L) and a sodium hydroxide aqueous solution (the molar concentration of sodium hydroxide was 1.25 mol / L); the mixture was added dropwise to a mixed solution of 12 g of anhydrous ethanol and 12 g of oleic acid while stirring at room temperature; then 10 mL of a sodium dihydrogen phosphate aqueous solution (the molar concentration of phosphate ions was 0.46 mol / L) was added dropwise to the above solution, mixed well, and placed in a microwave reactor. Under stirring conditions, a biomimetic mineralization reaction occurred at a reaction temperature of 140° C. and a reaction time of 30 minutes. After the reaction, the reaction precipitate was washed and dried to obtain hydroxyapatite nanowires;

[0107] Preparation of a dispersion containing hydroxyapatite nanowires: The hydroxyapatite nanowires were dispersed in water and shear-milled using a vacuum homogenizer (energy consumption per unit mass was 8 kWh / kg and the temperature was 25°C). The shear milling speed was 25 m / s and the shear milling time was 30 minutes. A dispersion containing hydroxyapatite nanowires was obtained (the solid content of the dispersion was 8 wt%).

[0108] Preparation of a polylactic acid fiber membrane coated with a polydopamine coating: 0.2 g of dopamine (CAS number: 51-61-6) was weighed and dissolved in a tris(hydroxymethyl)aminomethane buffer solution (pH 10, mass concentration of tris(hydroxymethyl)aminomethane) was 1 mg / mL) to obtain a dopamine-containing buffer solution, wherein the mass concentration of dopamine was 1 mg / mL.

[0109] The polylactic acid fiber membrane (fiber diameter of 12 μm, thickness of 0.1 mm) was immersed in the above-mentioned dopamine-containing buffer solution. The immersion treatment time was 24 h, the treatment temperature was 25°C, and the amount of dopamine-containing buffer solution used was 1200 mL per cubic meter of polylactic acid fiber membrane. After the immersion, excess buffer solution and impurities were removed, and after drying, a polylactic acid fiber membrane with a surface coated with a polydopamine coating was obtained.

[0110] Preparation of polylactic acid composite film: The dispersion containing hydroxyapatite nanowires prepared above is distributed on the surface of the polydopamine coating by electrophoretic deposition, and then dried to obtain the polylactic acid composite film.

[0111] The polylactic acid composite film prepared by the above preparation method comprises: the weight of hydroxyapatite nanowires in the polylactic acid composite film is 10wt%, the weight of the polydopamine coating in the polylactic acid composite film is 8wt%, the thickness of the polydopamine coating is 0.25μm; the diameter of the hydroxyapatite nanowires is 50nm; and the aspect ratio of the hydroxyapatite nanowires is 145:1.

[0112] Example 6

[0113] The difference from Example 3 is that the hydroxyapatite nanowires in this example are not subjected to shearing, grinding and dispersion treatment, and a dispersion containing hydroxyapatite nanowires is not prepared.

[0114] Specifically, hydroxyapatite nanowires and a polylactic acid fiber membrane coated with a polydopamine coating on the outer surface were prepared by the same preparation method as in Example 3. The hydroxyapatite nanowires were distributed on the surface of the polydopamine coating by vacuum filtration, and then dried to obtain a polylactic acid composite membrane.

[0115] Example 7

[0116] The only difference from Example 3 is that the diameter of the hydroxyapatite nanowires is 200 nm, and the aspect ratio of the hydroxyapatite nanowires is 5:1.

[0117] Example 8

[0118] The only difference from Example 3 is that the weight content of hydroxyapatite nanowires in the polylactic acid composite film is 50 wt %.

[0119] Example 9

[0120] The only difference from Example 3 is that the weight content of the polydopamine coating in the polylactic acid composite film is 20 wt %, and the thickness of the polydopamine coating is 500 nm.

[0121] Example 10

[0122] The only difference from Example 3 is that the thickness of the polylactic acid fiber film in the polylactic acid composite film is 1.3 mm.

[0123] Example 11

[0124] The only difference from Example 3 is that the thickness of the polylactic acid fiber film in the polylactic acid composite film is 0.02 mm.

[0125] Example 12

[0126] The only difference from Example 3 is that the fiber diameter of the polylactic acid fiber membrane in the polylactic acid composite membrane is 150 μm.

[0127] Example 13

[0128] The only difference from Example 3 is that the fiber diameter of the polylactic acid fiber membrane in the polylactic acid composite membrane is 0.5 μm.

[0129] Comparative Example 1

[0130] The difference from Example 3 is that the polylactic acid composite film of this embodiment does not include hydroxyapatite nanowires.

[0131] The specific preparation method is as follows: 0.2 g of levodopa (CAS No.: 59-92-7) is weighed and dissolved in tris (hydroxymethylaminomethane) buffer (pH 8.5, mass concentration of tris (hydroxymethylaminomethane) is 2 mg / mL) to obtain a buffer solution containing a dopamine derivative, wherein the mass concentration of levodopa is 2 mg / mL;

[0132] The polylactic acid fiber membrane (fiber diameter of 18 μm, thickness of 0.3 mm) was placed in the above-mentioned buffer solution containing dopamine derivatives for immersion. The immersion treatment time was 12 h, the treatment temperature was 25 ° C, and the amount of the buffer solution containing dopamine derivatives was 1200 mL per cubic meter of polylactic acid fiber membrane. After the immersion, the excess buffer solution and impurities were removed. After drying, a polylactic acid fiber membrane with a polydopamine coating on the outer surface was obtained, which was a polylactic acid composite membrane.

[0133] Comparative Example 2

[0134] The difference from Example 4 is that the polylactic acid composite film of this embodiment does not include a polydopamine coating.

[0135] Specifically, hydroxyapatite nanowires and a dispersion containing hydroxyapatite nanowires were prepared using the same preparation method as in Example 3. The dispersion containing hydroxyapatite nanowires was distributed on the surface of a polylactic acid fiber membrane by suction filtration, and then dried to obtain a polylactic acid composite membrane.

[0136] Structural characterization and performance testing

[0137] Scanning electron microscope observation: The microstructure of the hydroxyapatite nanowires synthesized in Example 3 was observed by field emission scanning electron microscope (model JSM-7900F, Japan Electronics). Figure 2 As shown), and the microstructure of the hydroxyapatite nanowires in the dispersion containing hydroxyapatite nanowires after the hydroxyapatite nanowires synthesized in Example 3 were treated by liquid phase circulating high-speed shear grinding technology (as shown Figure 3 shown).

[0138] Tensile Properties: The resulting fiber membranes were cut into tensile specimens. The tensile properties of the composites were tested using an Instron universal tensile tester (Model 4403, 100N sensor) according to ASTM D638-2003, the American Society for Testing and Materials standard for tensile properties of plastics. At least three parallel test specimens were tested for each group, and the average of the results was calculated.

[0139] Surface potential test: A non-contact electrostatic meter (VM54XQS, Quatek, USA) was used to test the surface potential of the micron fiber membrane (area 100mm 2 ), the test height was 2 cm, the temperature and humidity were constant at 25°C and 45%, and 20 data points were randomly collected for each sample and the average value was taken.

[0140] Filtration performance test: LZC-K automatic filter material tester (Suzhou Huada Instrument Equipment Co., Ltd.) was used to test the micron fiber membrane (area 100cm 2The air filtration performance of the membrane was measured at a flow rate of 85 L / min. The aerosol generator produced NaCl atomized particles with a particle size range of 0.1 to 10 μm. Each fiber membrane set was tested at least three different locations, and the results were averaged.

[0141] The above test results are shown in Table 1.

[0142] Table 1

[0143]

[0144] The hydroxyapatite nanowires synthesized by microwave-assisted biomimetic mineralization have good structural regularity and crystallinity and the aspect ratio is also well controlled, which lays the structural foundation for it to be used as a bioelectret. At the same time, combined with the liquid phase circulation high-speed shear grinding technology, a good dispersion morphology (such as Figure 3 In sharp contrast, the hydroxyapatite nanowires that have not been treated by the liquid phase circulating high-speed shear grinding device have obvious agglomeration and are difficult to obtain a well-dispersed morphology (as shown in FIG. Figure 2 shown).

[0145] Table 1 shows the tensile test, surface potential test, and filterability test results of the polylactic acid composite membranes of the embodiments of the present invention and the comparative examples. It can be seen from the table that Examples 1-5 and Examples 7-10 all have relatively high breaking strengths (45 MPa to 65 MPa), reflecting excellent mechanical properties and fully meeting the mechanical performance requirements of polylactic acid fiber membranes in the field of filter materials. However, the breaking strengths of Examples 11-13 are 12 to 35 MPa. This is because the thickness of the polylactic acid fiber membranes of Examples 11-13 is too low, or the diameter of the polylactic acid fiber membranes is too large or too small, which is not conducive to the attachment and dispersion of the polydopamine coating and hydroxyapatite nanowires on the fiber surface, resulting in a significant decrease in their mechanical properties, but they still have certain application possibilities. The breaking strength of Comparative Examples 1 to 2 and Example 6 is significantly lower than that of Example 3 (41 MPa to 45 MPa). This is mainly because Comparative Example 1 does not include a bioelectret, which reduces the mechanical properties, and the polylactic acid composite film of Comparative Example 2 does not include a polydopamine coating, resulting in a low binding force between hydroxyapatite nanowires and polylactic acid, which reduces the mechanical properties. The polylactic acid fiber film of Example 6 has not undergone shear grinding and dispersion treatment, resulting in a certain agglomeration of hydroxyapatite nanowires, resulting in more stress concentration points in the fibers, thereby reducing the mechanical properties.

[0146] It is also of great significance that Examples 1 to 5 all exhibit extremely high surface potentials (5.2kV to 12.9kV) and show almost no decay over time, confirming their extremely high long-term stability. In particular, the initial value of the surface potential of Example 3 is as high as 12.9kV, which is 2.39 times that of Comparative Example 1 and 1.93 times that of Comparative Example 2; and after 90 days, the surface potential of Example 3 remains at 12.8kV, while Comparative Examples 1 and 2 significantly decay to 0.5kV and 0.2kV. This is because the polylactic acid composite film of Example 3 includes both a polydopamine coating and hydroxyapatite nanowires. Under the action of the polydopamine coating, the hydroxyapatite nanowires can be evenly dispersed, giving full play to the polarization or charging properties of the hydroxyapatite nanowires. However, Comparative Example 1 does not contain hydroxyapatite nanowires, and the polylactic acid composite film has no bioelectret, resulting in a significant decrease in its surface potential; and the polylactic acid composite film of Comparative Example 2 does not have the connecting effect of the polydopamine coating on the hydroxyapatite nanowires, so that the hydroxyapatite nanowires are unevenly dispersed on the surface of the polylactic acid fiber membrane and are easy to agglomerate, and the hydroxyapatite nanowires are not easy to exert polarization or charging properties.

[0147] Since the dispersion degree of bioelectret in the fiber membrane and the surface potential of the polylactic acid microfiber membrane are closely related to the filtration performance, Example 3 with the highest surface potential performed best in the filtration test. 0.3 and PM 2.5 The filtration efficiency reached 99.7% and 99.9% respectively, which was much higher than that of the comparative examples 1 and 2 (PM 0.3 and PM 2.5 The filtration efficiency is less than 90%).

[0148] PM of Examples 6 to 13 0.3 The filtration effect (75.4-91.7%) was lower than that of Example 3, mainly because the uneven attachment of hydroxyapatite nanowires on the fiber surface caused the fiber surface potential to decrease, resulting in the poor performance of PM filtration. 0.3 The electrostatic adsorption effect is weakened; PM of Examples 6 to 13 2.5 The filtration efficiency (75.6-93.2%) of Example 3 is lower than that of Example 3, mainly because the low interfacial bonding force between polylactic acid fiber and hydroxyapatite nanowires causes the surface potential of the fiber membrane to decrease over time, or the thickness and diameter of the polylactic acid fiber are too high or too low and the aspect ratio of the hydroxyapatite nanowire is too small, which leads to a decrease in the physical interception efficiency of the polylactic acid fiber composite membrane, resulting in a decrease in PM 2.5 The filtration efficiency is reduced.

[0149] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: (1) the structural regularity and uniformity of hydroxyapatite nanowires synthesized by microwave-assisted biomimetic mineralization are improved, so that they are evenly dispersed on the polylactic acid composite membrane, thereby better exerting the function of the bioelectret; (2) a dispersion containing hydroxyapatite nanowires is prepared, and the hydroxyapatite nanowires are sheared and ground to promote the surface activation of the hydroxyapatite nanowires and the ability to disperse evenly in the dispersion, so that they are evenly distributed on the surface of the polyamine coating, thereby effectively exerting the function of the bioelectret; (3) by coating the surface with polydopamine, the hydrophobicity of polylactic acid is improved, and the interfacial bonding force between the bioelectret and the polylactic acid fiber membrane is improved, so that it can achieve an extremely high and long-lasting surface potential, which helps to improve the filtration efficiency of the fiber membrane and has good application prospects.

[0150] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A polylactic acid composite film, comprising a polylactic acid fiber film, characterized in that: The surface of the polylactic acid fiber membrane is coated with a polydopamine coating, and the surface of the polydopamine coating is distributed with hydroxyapatite nanowires; The weight content of the hydroxyapatite nanowires in the polylactic acid composite film is 0.05-40 wt %; the weight content of the polydopamine coating in the polylactic acid composite film is 0.01-10 wt %; The thickness of the polylactic acid fiber membrane is 40-800 μm, and the fiber diameter of the polylactic acid fiber membrane is 5-60 μm; Distributing the dispersion containing hydroxyapatite nanowires on the surface of the polydopamine coating by one or more methods including atomization, vacuum filtration, immersion, or electrophoretic deposition; The dispersion containing hydroxyapatite nanowires is obtained by the following preparation method: dispersing hydroxyapatite nanowires in a dispersant and performing shear grinding to obtain the dispersion containing hydroxyapatite nanowires.

2. The polylactic acid composite film according to claim 1, characterized in that The weight content of the hydroxyapatite nanowires in the polylactic acid composite film is 0.5-20 wt %.

3. The polylactic acid composite film according to claim 1, characterized in that The weight content of the polydopamine coating in the polylactic acid composite film is 0.1-5 wt %.

4. The polylactic acid composite film according to any one of claims 1 to 3, characterized in that The thickness of the polydopamine coating is 40-300 nm.

5. The polylactic acid composite film according to any one of claims 1 to 3, characterized in that The diameter of the hydroxyapatite nanowires is 1-200 nm.

6. The polylactic acid composite film according to any one of claims 1 to 3, characterized in that The aspect ratio of the hydroxyapatite nanowires is 5-200:

1.

7. The polylactic acid composite film according to any one of claims 1 to 3, characterized in that The aspect ratio of the hydroxyapatite nanowires is 80-150:

1.

8. A method for preparing a polylactic acid composite film according to any one of claims 1 to 7, characterized in that: The preparation method comprises: Providing polylactic acid fiber membrane; A polydopamine coating is provided on the surface of the polylactic acid fiber membrane; The hydroxyapatite nanowires are distributed on the surface of the polydopamine coating to obtain the polylactic acid composite film.

9. The method for preparing a polylactic acid composite film according to claim 8, wherein: The preparation method comprises: placing the polylactic acid fiber membrane in a buffer solution containing dopamine and / or dopamine derivatives for immersion, so that the dopamine and / or the dopamine derivatives are polymerized to generate polydopamine, and the polydopamine is coated on the surface of the polylactic acid fiber membrane, and after drying, the polylactic acid fiber membrane with the surface coated with the polydopamine coating is obtained.

10. The method for preparing a polylactic acid composite film according to claim 9, wherein: The immersion treatment time is 4 to 36 hours, and the treatment temperature is 25 to 60°C.

11. The method for preparing a polylactic acid composite film according to claim 9, wherein: The amount of the buffer solution used is 100-3000 mL per cubic meter of the polylactic acid fiber membrane.

12. The method for preparing a polylactic acid composite film according to claim 9, wherein: The amount of the buffer solution used is 1000-2500 mL per cubic meter of the polylactic acid fiber membrane.

13. The method for preparing a polylactic acid composite film according to claim 9, wherein: The mass concentration of the dopamine and / or the dopamine derivative in the buffer solution is 0.5-100 mg / mL.

14. The method for preparing a polylactic acid composite film according to claim 9, wherein: The mass concentration of the dopamine and / or the dopamine derivative in the buffer solution is 0.5-30 mg / mL.

15. The method for preparing a polylactic acid composite film according to claim 9, wherein: The solvent in the buffer solution is tris(hydroxymethyl)aminomethane buffer.

16. The method for preparing a polylactic acid composite film according to claim 15, characterized in that: The pH of the tris(hydroxymethyl)aminomethane buffer is 8-10.

17. The method for preparing a polylactic acid composite film according to claim 9, wherein: The dopamine derivative is selected from one or more of dopamine hydrochloride, N-methyl dopamine, and 3-methacryloyl dopamine.

18. The method for preparing a polylactic acid composite film according to any one of claims 8 to 17, characterized in that: The dispersion containing hydroxyapatite nanowires is distributed on the surface of the polydopamine coating by adopting one or more methods of atomization, vacuum filtration, immersion or electrophoretic deposition.

19. The method for preparing a polylactic acid composite film according to claim 18, wherein: The dispersion containing hydroxyapatite nanowires is obtained by the following preparation method: dispersing hydroxyapatite nanowires in a dispersant and performing shear grinding to obtain the dispersion containing hydroxyapatite nanowires.

20. The method for preparing a polylactic acid composite film according to claim 19, wherein: The dispersant is selected from one or more of ethanol, water, polyvinyl pyrrolidone, dodecyltrimethylammonium bromide, sodium lauryl sulfate or sodium dodecylbenzenesulfonate.

21. The method for preparing a polylactic acid composite film according to claim 19, wherein: The linear speed of the shear grinding is 15-40 m / s; and the time of the shear grinding is 10-120 min.

22. The method for preparing a polylactic acid composite film according to claim 18, wherein: The solid content of the dispersion containing hydroxyapatite nanowires is 1-15 wt %.

23. The method for preparing a polylactic acid composite film according to claim 19, wherein: The shear grinding is performed in a high-speed shear grinding device, and the energy consumption per unit mass of the high-speed shear grinding device is 0.5-10 kWh / kg.

24. The method for preparing a polylactic acid composite film according to claim 23, wherein: The high-speed shearing and grinding equipment is one or more of a shearing emulsifier, a pipeline shearing and dispersing emulsifier, a vacuum homogenizing emulsifier, a pin-type sand mill or a turbine sand mill.

25. The method for preparing a polylactic acid composite film according to any one of claims 8 to 17, characterized in that: The hydroxyapatite nanowires are prepared by the following method: fatty acid, alcohol solvent, alkaline solution, water-soluble calcium salt solution and water-soluble phosphate solution are mixed and placed in a microwave reactor for biomimetic mineralization reaction to obtain the hydroxyapatite nanowires.

26. The method for preparing a polylactic acid composite film according to claim 25, wherein: The fatty acid and the alcohol solvent are first mixed, and then the alkaline solution and the water-soluble calcium salt solution are added under stirring conditions to react to generate a fatty acid calcium precursor; then the fatty acid calcium precursor and the water-soluble phosphate solution are mixed and placed in the microwave reactor, and the biomimetic mineralization reaction is carried out under stirring conditions to obtain the hydroxyapatite nanowires.

27. The method for preparing a polylactic acid composite film according to claim 25, wherein: The fatty acid is selected from one or more of stearic acid, lauric acid, oleic acid, linoleic acid or linolenic acid.

28. The method for preparing a polylactic acid composite film according to claim 25, wherein: The alcohol solvent is selected from one or more of ethanol, methanol, propanol, isopropanol or butanol.

29. The method for preparing a polylactic acid composite film according to claim 25, wherein: The alkaline solution is selected from a sodium hydroxide aqueous solution, and the molar concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 0.01-10 mol / L.

30. The method for preparing a polylactic acid composite film according to claim 25, wherein: The water-soluble calcium salt solution is selected from one or more of a calcium chloride aqueous solution, a calcium nitrate aqueous solution, a calcium acetate aqueous solution or a calcium hypochlorite aqueous solution.

31. The method for preparing a polylactic acid composite film according to claim 25, wherein: The water-soluble phosphate solution is selected from one or more of an aqueous solution of ammonium dihydrogen phosphate, an aqueous solution of sodium dihydrogen phosphate, an aqueous solution of dipotassium hydrogen phosphate or an aqueous solution of potassium dihydrogen phosphate.

32. The method for preparing a polylactic acid composite film according to claim 25, wherein: The molar concentration of calcium ions in the water-soluble calcium salt solution is 0.01-2 mol / L.

33. The method for preparing a polylactic acid composite film according to claim 25, wherein: The molar ratio of calcium ions in the water-soluble calcium salt solution to phosphate ions in the water-soluble phosphate solution is 1-2:

1.

34. The method for preparing a polylactic acid composite film according to claim 25, wherein: The reaction temperature of the biomimetic mineralization reaction is 100-250° C., and the reaction time is 1-60 minutes.

35. Use of the polylactic acid composite membrane according to any one of claims 1 to 7 or the polylactic acid composite membrane obtained by the preparation method according to any one of claims 8 to 34 in an air filter material.

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